The present invention relates to desulfurization of metal-contaminated heavy oils using fixed catalyst beds, and particularly to an overall hydrodesulfurization process wherein the catalyst is periodically removed from the reactor and then replaced with fresh catalyst.
Hydrodesulfurization is a well-known process. In general, it involves contacting oils at elevated temperatures and pressures with a catalyst to convert organic sulfur compounds to sulfur-free hydrocarbons and hydrogen sulfide. The hydrogen sulfide can be readily removed from the hydrocarbons and the reduced sulfur content hydrocarbons are a more desirable fuel in the sense of creating less sulfur oxides upon combustion. Also, the desulfurized hydrocarbons are improved feed materials for further refinery processing, such as hydrocracking or catalytic cracking or other upgrading refining processing. The hydrodesulfurization can be carried out in conjunction with other hydrotreating, such as hydrodenitrification and/or hydrodemetalation.
Catalysts used in hydrodesulfurization are well known. They typically include Group VI metals and/or Group VIII metals on a refractory support, such as alumina or silica or alumina-silica compositions. Examples of hydrodesulfurization catalysts are given in the following patents, the disclosures of which are incorporated herein by reference: U.S. Pat. No. 4,564,439; U.S. Pat. No. 4,495,308; U.S. Pat. No. 4,443,558; U.S. Pat. No. 4,066,574; U.S. Pat. No. 4,051,021; and U.S. Pat. No. 4,006,076.
The present invention is particularly directed to a fixed bed hydrodesulfurization process as opposed to a fluidized or ebullated or a moving bed process. Fixed bed hydrodesulfurization processes, and reactors therefor, are well known. See, for example, Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd Edition, Vol. 19 at page 908; also Vol. 17 at page 201 to page 205.
Removal of catalysts from fixed bed reactors is typically done by opening the reactor and vacuuming catalyst particles out of the top of the reactor or removing closures from certain openings in the bottom part of the reactor and then allowing the catalysts to flow out of the reactors, much like grain might flow out of a silo.
Other means disclosed for removing catalysts include a published Japanese patent application, 84JP-274409, which discloses removal of a caked together exhausted catalyst from a reactor by (1) making a hole in the catalyst material, (2) filling the hole, in the presence of water, with a hydratable, expansive crumbling agent, (3) leaving the catalyst until it has been crumbled, and (4) removing the crumbled catalyst from the reactor.
U.S. Pat. No. 3,775,805 discloses a method and apparatus for clearing solid materials such as catalysts from elongated hollow structures, for example, catalyst-filled tubes of a steam methane reformer, by inserting into the hollow tubes a drill bit connected to a drive motor by a hollow drill stem, operating the motor to rotate the bit and break up the catalyst and simultaneously withdraw broken up catalysts by the application of vacuum to the interior of the drill stem which is in communication with the interior of the hollow structure of the apertures in the drill bit body.
In a different field, namely, coking for the production of coke and coker gas oil, coke, as opposed to catalyst, has been removed by methods involving drilling. In coke production processes, coke is removed from coke production vessels, which vessels are essentially completely hollow and contain no internals such as support means for fixed catalyst beds. See, for example, U.S. Pat. No. 3,880,357 which discloses apparatus for decoking the coke drum of a delayed coker after a vertical central hole has been cut. The U.S. Pat. No. 3,880,357 apparatus comprises a rotatable and vertically movable drill stem carrying water under pressure to nozzles supplying downward jet streams, the nozzles and the drill stems being mechanically linked to enable the radius of action of the jet streams to be incrementally increased while maintaining the nozzles vertical, so that the coke is removed in a series of cylindrical sections.
Similarly, at page 108 of the Oil and Gas Journal, May 17, 1982, a method is disclosed for decoking a shale oil recovery vessel. According to that method, the decoking system first guides a spinning head with water jets into the solid mass of coke. The jets bore a hole three to four feet in diameter in the center of the coke to the bottom of the tank. Then the boring head retracts and a cutting head is installed. Coke is cut into small chunks by the high pressure water jets so that it can be washed away through the bottom of the tank. The water in the system is recycled.
Coking operations are substantially different from catalytic hydrodesulfurization operations in that the coking operation is carried out without catalyst and without reactor internals that are required in catalytic hydrodesulfurization processes. One method which has been used to assist in catalyst removal where the catalyst is caked together due to interstitial deposits is to attempt to wash the deposits away sufficiently, using a heated mid boiling range oil, so that the catalyst will be sufficiently free to flow out the reactor through a bottom opening, or be vacuumed from the top of the reactor. However, in many instances this approach helps but is not sufficient so that the catalyst will flow to catalyst beds in a reactor that has been used for hydrodesulfurization of heavy feeds such as vacuum residuum.